Mechanisms of fatigue are not well understood in the elderly. Current tools for assessing fatigue do not include QOL items reflecting objective measurement of neurophysiologic and cognitive impairment. Aging and age-related disease are often associated with decreased physical and social activity and cognitive function, as well as an increase in perceived levels of fatigue. This is characterized by symptoms of general weakness, loss of muscle strength, impaired mobility and balance, increased fall risk, and poor endurance. Fatigue is not necessarily a symptom of a medical disease state but may be due to fatigue of physical or mental functioning. Given the increasing proportion of older people suffering from decline in somatic and autonomic function, sarcopenia, changes in emotion, pain and depression, the primary aim of this proposal is to develop a quality of life (QOL) tool for assessing fatigue in older individuals. To create this tool, we plan to use the 96 PROMIS item pool as well as the 42-item pool constructed in Norfolk, that reflect the mental and physical components of fatigue. Our multidisciplinary team has experience in developing domain specific quality of life tools and has the clinical expertise and track record to successfully evaluate physical, neurovascular, somatic, and autonomic function, pain, insomnia and cognitive dysfunction in older individuals. The ultimate aim is to ensure that the newly derived fatigue QOL item pool will be sensitive to mental and physical elements of fatigue determined with objective stressors. To develop, refine, and validate this tool, a total of 400 participants, ages 20-85 will be asked to respond to the preliminary fatigue item pool. Item analysis, exploratory, and confirmatory factor analysis will be used to characterize and evaluate the factor structure of the fatigue tool. Moreover, these analyses will allow for the selection of the smallest set of items that can still effectively measure the identified components of fatigue. The newly distilled tool will be administered to a subset of 75 subjects who will complete a series of questionnaires to determine their level of physical activity, fear of falling, and perceived levels of activity and the relationship to objective measures of physical and cognitive fatigue during voluntary everyday movements (e.g. balance and gait) using simple choice and reaction time, exercise-induced physical, somatic and autonomic nervous system fatigue as well as mental stressors to test cognitive fatigue. The PROMIS/Norfolk QOL fatigue tool will be an instrument capable of discerning the presence of fatigue, and be sensitive to the role that cognitive and physical factors play in older individuals' well being. It will be reduced to the minimum number of questions to be viable in the clinic yet retain its ability to discriminate mental and physical fatigue and the components, which contribute to fatigue. Ultimately, this new tool will serve the need to test the potential of therapeutic agents in clinical trials to relieve fatigue.